Manufacture of rubber-impregnated products



Patented Mar. 14, 1933' UNITED STATES PATENT OFFICE GEORGE A. RICHTER,WALLACE 1B. VAN ARSDEL, AND ROGER B. BILL, OF BERLIN, HAMPSHIRE,ASSIGNORS TO BROWN COMPANY, OF BERLIN, NEW HAMPSHIRE, A.

CORPORATION OF MAINE MANUFACTURE OF RUBBER-IMPREGNATED PRODUCTS NoDrawing.

Rubber latex asfound in nature consists of a dispersion of rubberglobules in an aquef ous medium or serum, the dispersion being complexin its nature in that it contains various non-rubber solids such asresins, proteins, sugars, and mineral matters. The amount of non-rubbersolids associated with a latex depends upon such factors as the specieof rubber tree from which it is derived, the age of the tree, and theseason of the year when the tree is tapped, but it has been found byvarious investigators that a rubber latex derived from the Heceabmsz'lz'encz's and having a total solids content of about 38% maycontain 4%, more or less, non-rubber solids, the chief components 'ofwhich are proteinand resinous bodies. Rubber latex, therefore, in itsnatural condition is a crude or impure raw material in the sense that itcontains a substantial amount of non-rubber solids, in addition torubber.

There are various uses to which rubber latex is put, according to whichthe aqueous content of the latex is removed, leaving behind a rubbercompound containing the non- I rubber solids present in the originallatex.

For instance, rubber latex is sometimes used to impregnate porousmaterials, to lmpart desirable characteristics thereto, the use ofrubber in this form sometimes being more economical .and giving betterresults than the use of so-called rubber organic solvent solutions forthis purpose,"and being further advantageous in that it does away withfire hazard. It is sometimes the practice to impregnate fibrous materialin the" form of strand material such'as cords, woven fabrics, or webs ofcellulose fibers such as cotton or Wood pulp, and then to dry and, ifdesired, to vulcanize the impregnated product to impartwater repellencyor other desirable characteristics thereto. When a porous web ofcellulose fiber interfelted on machinery of the papermaking type isimpregnated with rubber latex, then dried and, if desired, vulcanized,it is found that the product acquires characteristics includingstrength, stretch, .tear. resistance, pliability and feel, simulatingthose .of natural leather. The closeness with which artificial leatherApplication filed April 22,

sheetings made as herein described come to the natural product dependsupon various factors, but it has been found that by choosing theappropriate fibrousbase, impregnating it with latex, and then drying, itis possible to produce artificial leather sheetings eminentlysatisfactory for use as a substi- 'tute for the natural product in manyfields.

The fibrous base found most suitable is one composed. of interfeltedabsorfptige; fillierii ne to ig v cial uses, harshness and stifiness 1nleathers 1 are decidedly disadvantageous, but if it is attempted to doaway with these characteristics as by compounding the rubber content ofthe sheeting with various softening or plasticizing agents such as oilsor waxes, it is generally found that if suflicient of such a ents beused to effect a decided softening, t e stren h of the sheeting isseriously impaired. e have found that harshness and stiffness in thefinished product may be partly ascribed to the non-rubber solids presentin the latexused for impregnation and remaining behind along with therubber in the sheeting after the aqueous content of the latex isremoved. We have further found that if by so doing the non-rubbersolidsare caused to work to the surface, from'wliich they may be removed bythe chemical solution or during subsequent washing, and the sheeting ismade remarkably flexible. 'The preferable tion, the more efl'ective hasbeen found to be the action of a solution of caustic soda of a. givenstrength, indicating that the treatment might be analogous to themercerizing action of caustic soda on cellulose. So far as we haveobserved, however, there is apparently no mercerizing action,ion-instead of producing a spongy, puffy sheet as would be expected ifmercerization occurred, the ac tion of the caustic soda solution is tocom pact the sheeting somewhat. In actual practice, the sheeting may bepassed through a bath of caustic soda solution under the conditions ofcausic soda concentration and temperature previously given, the time ofcontact with the bath being, say, tenminutes, whereupon the sheeting maybe mechanically worked while wet with the caustic soda solution, as thistends to enhance pliability and softness of, feel in the finishedproduct, and at the same time diminish its. tackine'ss and increase'itsstrength. After such treatment, the caustic soda solution remaining inthe sheeting should be removed by washing with water, whereupon thewashed sheeting may be dried and subjected to the desired finishingtreatments.

While we cannot state with precision the chemical action of caustic sodaon the nonrnbber solids present in rubber-impregnated sheeting, such asdescribed, it is our theory that the caustic soda, particularly undermechanical working of the sheeting, may eifect a saponificatlon of thesaponifiable resins to form soluble, soap-like compounds, and may alsoreact upon proteins to form soluble proteinates, while at the same timethe water serves to dissolve sugars and water-soluble minerals which areexposed to the action of the aqueous solution by the mechanical working.Other strong alkalies, such as caustic potash, are equivalent in theiraction to caustic soda, and there are other chemical solutions, such asstrong solutions of zinc chloride and calcium or lithium thiocyanate,which act largely upon and dissolve the proteins, probably effectinglittle, if any, reaction upon the resins.

The process of the present invention may be advantageously practisedwhen latices either in natural condition or in which the rubber globuleshavebeen vulcanized, as by the Schidrowitz process, are used as a rawmaterial, but there is little 9! no advantage in carrying out theprocess herein described when a latex purified in the sense thatnonrnbber solids have beenremoved therefrom is used as a raw material,the globules of such latex being either in a natural or vulcanizedcondition. The process may also be used after a latex-treated sheet hasbeen Vulcan ized. This vulcanization may be brought about either bydipping the-sheet for a few minutes in a dilute solution of sulphurchloride in an inert solvent such as carbon tetrachloride or bycompounding with" the latex the appropriate vulcani'zing'ingredientssuch assulphur and an accelerator and then heating the sheet to atemperature which will cause vulcanization. If the vulcanized sheet istreated with a chemical solution such as caustic soda in the mannerdescribedythere is some increase in. strength and softness; and thealkali tendstrr remove acidity-or any excess sulphur. .lVe do not hereinclaim per se the mechanical working of rubber-impregnatedfibroussl1eeting.while wet, as this subject matter is disclosed 'andclaimed in a plication Serial No.- 358,745, filed April 2 7,

1929, by: Roger B. Hill a n'dJohn A. Fogarty.

lFVe claim I 1; A process which comprises impregnatingf fibroussheetmaterial with rubber latex, drying, treating with a caustic sodasolution to remove resins and proteins associated with the latex,mechanically working the sheeting while met with the chemical solution,washing free of chemical solution, and drying.

2. A process whichcomprises' impregnating fibrous sheet material withrubber latex, drying, treating with sulphur chloride to effectvulcanization, mechanically working the sheet while wet with causticsoda solution, washing free of chemicalsolution, and dry- A processwhich comprises impregnating a'felted fibrous sheet with rubber-latex;drying the latex-impregnated sheet; mechanically working the dried,latex-impregnated sheet with an aqueous solution of a chemical selectedfrom a group consisting of caustic soda, caustic potash, zinc chloride,calicum thiocyanate, and lithium thio-' cyanate to dissolvewater-insoluble, n'onrubber solids, including resins and proteins, andto cause them to appear on the surface of the sheet; washing the sheetfree from chemical solution and dissolved solids; and drying the sheet.v

In testimony whereof we have aflixed our signatures.

GEORGE A. RICHTER. WALLACE B. VAN ARSDEL. ROGER B. HILL.

